| Message ID | 20150317161958.991bd7dc36c714f6498821db@lab.ntt.co.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 17/03/2015 08:19, Takuya Yoshikawa wrote: > When all bits in mask are not set, > kvm_arch_mmu_enable_log_dirty_pt_masked() has nothing to do. But since > it needs to be called from the generic code, it cannot be inlined, and > a few function calls, two when PML is enabled, are wasted. > > Since it is common to see many pages remain clean, e.g. framebuffers can > stay calm for a long time, it is worth eliminating this overhead. > > Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> > --- > virt/kvm/kvm_main.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index a109370..420d8cf 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1061,9 +1061,11 @@ int kvm_get_dirty_log_protect(struct kvm *kvm, > mask = xchg(&dirty_bitmap[i], 0); > dirty_bitmap_buffer[i] = mask; > > - offset = i * BITS_PER_LONG; > - kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset, > - mask); > + if (mask) { > + offset = i * BITS_PER_LONG; > + kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, > + offset, mask); > + } > } > > spin_unlock(&kvm->mmu_lock); > Good catch! Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Mar 17, 2015 at 09:58:21AM +0100, Paolo Bonzini wrote: > > > On 17/03/2015 08:19, Takuya Yoshikawa wrote: > > When all bits in mask are not set, > > kvm_arch_mmu_enable_log_dirty_pt_masked() has nothing to do. But since > > it needs to be called from the generic code, it cannot be inlined, and > > a few function calls, two when PML is enabled, are wasted. > > > > Since it is common to see many pages remain clean, e.g. framebuffers can > > stay calm for a long time, it is worth eliminating this overhead. > > > > Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> > > --- > > virt/kvm/kvm_main.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index a109370..420d8cf 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -1061,9 +1061,11 @@ int kvm_get_dirty_log_protect(struct kvm *kvm, > > mask = xchg(&dirty_bitmap[i], 0); > > dirty_bitmap_buffer[i] = mask; > > > > - offset = i * BITS_PER_LONG; > > - kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset, > > - mask); > > + if (mask) { > > + offset = i * BITS_PER_LONG; > > + kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, > > + offset, mask); > > + } > > } > > > > spin_unlock(&kvm->mmu_lock); > > > > Good catch! > > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index a109370..420d8cf 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1061,9 +1061,11 @@ int kvm_get_dirty_log_protect(struct kvm *kvm, mask = xchg(&dirty_bitmap[i], 0); dirty_bitmap_buffer[i] = mask; - offset = i * BITS_PER_LONG; - kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, offset, - mask); + if (mask) { + offset = i * BITS_PER_LONG; + kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot, + offset, mask); + } } spin_unlock(&kvm->mmu_lock);
When all bits in mask are not set, kvm_arch_mmu_enable_log_dirty_pt_masked() has nothing to do. But since it needs to be called from the generic code, it cannot be inlined, and a few function calls, two when PML is enabled, are wasted. Since it is common to see many pages remain clean, e.g. framebuffers can stay calm for a long time, it is worth eliminating this overhead. Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> --- virt/kvm/kvm_main.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)